Circuit arrangement for increasing the efficiency
of an electron tube type amplifier



June 28, 1966 N c 3,258,710

CIRCUIT ARRANGEMENT FOR INCREASING THE EFFICIENCY OF AN ELECTRON TUBE TYPE AMPLIFIER Filed Sept. 6, 1965 5 Sheets-Sheet 1 v 2 500%az7 a Hg. 2

INVENTOR ER/ CH #:nvacxe BY Aw ATTORNEY June 28, 1966 E. HEINECKE 3,258,710

CIRCUIT ARRANGEMENT FOR INCREASING THE EFFICIENCY OF AN ELECTRON TUBE TYPE AMPLIFIER Filed Sept. 6, 1963 5 Sheets$heet 2 Fig-3 INVENTOR ERIC/7' HE/NEC/(f ATTORNEY June 28, 1966 HElNECKE 3,258,710

CIRCUIT ARRANGEMENT FOR INCREASING THE EFFICIENCY OF AN ELECTRON TUBE TYPE AMPLIFIER Filed Sept. 6, 1963 5 Sheets-Sheet 5 INVENTOR R/CH Hf/NECKE 1/ BY 12 7i,

ATTORNEY United States Patent 3,258,710 CIRCUIT ARRANGEMENT FOR INCREASING THE EFFICIENCY OF AN ELECTRON TUBE TYPE AMPLIFIER Erich Heinecke, Berlin, Germany, assignor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed Sept. 6, 1963, Ser. No. 307,210 Claims priority, application Germany, Sept. 20, 1962, St 19,736; Sept. 27, 1962, St 19,766 11 Claims. (Cl. 330-423) The present invention relates to a circuit arrangement for increasing the efficiency of an electron tube type amplifier for a modulated carrier frequency voltage.

The efficiency of a tube type amplifier is dependent upon the anode or plate voltage utilization, and the current utilization factor. In addition, the operating point determines the linearity as well as the efiiciency, particularly for class B-amplifiers. A normal amplifier of this type has a current factor of 1.57 and a voltage factor of about 0.9, which limits the efficiency to It is therefore an object of the present invention to provide an amlifier of improved efficiency. The novelty resides in the fact that the anode or plate operating voltage is composed of a direct voltage and a superimposed auxiliary AC. voltage having a frequency of double the value of the frequency of the carrier voltage. The amplitude of the auxiliary AC. voltage remains unchanged, and is thus independent of the modulation, and is chosen so that in the event of maximum modulation of the tube by the signal, and at a peak anode current, there will remain a predetermined anode voltage, and that at the desired conduction period, where the anode current just becomes zero, this remaining anode voltage is very small. In the case of tetrodes it is of advantage to employ the, same measure at the screen grid, 'so that in the same period there will only be available either a small or no screengrid voltage at all.

One particular advantage of the circuit arrangement which is especially effective for tetrodes, is the deformation of the anode-current characteristic with respect to the control voltage of the tube. Accordingly, there will result a reduction or diminution of the operating angle or conduction period of the anode current with respect to the input or control voltage and, consequently, an improvement of the current factor of the basic wave amplitude with respect to direct current. In this case the negative control grid bias will have to be adjusted in such a way that in the case of a low anode residual current the output characteristic which is dependent upon the control grid, will have a linear response. This adjustment will approximately result in an operating angle of 60, hence class C-operation, as well as in a current factor of 1.76.

The invention is also applicable to push-pull amplifiers wherein the maximum efficiency of a normal class B amplifier operating linearly and without distortion, is predetermined and amounts to about 65%. The added AC. voltage of twice the frequency is supplied by an additional class B amplifier whose input is fed with a voltage derived from the full-wave rectification of the input signal of the push-pull amplifier. The details of the invention and other objects and advantages will be explained more fully by reference to the following examples and drawings, in which:

FIG. 1 shows the current and voltage waveforms of the novel amplifier circuit;

FIG. 2 shows a basic circuit diagram;

3,258,710 Patented June 28, 1966 FIG. 3 shows an example of a quiescent push-pull amplifier and the additional amplifier;

FIG. 4 shows a modification of part of the circuit arrangement according to FIG. 3; and

FIG. 5 shows a circuit arrangement in which the invention is applied to a high-frequency resonance amplifier.

As shown in FIGS; 1 and 2 for example, at a transmitted high-frequency output of 200 kw., with a direct voltage source, V of 9500 v., the anode load is approximately 160 kw. and the double frequency alternating voltage, 11 of 5500 v. produces approximately 60.4 kw., which corresponds to an anode input of approximately 220.0 kw. and to an anode efliciency of approximately 91%. The screen grid 2 is coupled to a 500 V. DO supply, VgZ, with an added 1000 v., A.C., v of twice the signal frequency. In this case the tube would normally be operated with a plate voltage of 15,000 volts and screen grid voltage of 1500 volts, with a normal elficiency of 70.5% at the anode 1. Relative thereto it is to be considered that in this particular example, the tube, at its peak or maximum amplitude value, still has the required high remaining potential of 1500 volts.

When considering that the additional doubled frequency anode AC. voltage v is produced with the aid of a separate tube R0 operated at voltage saturation, with a total network efiiciency of about then the input of 60 kw. is increased to or kw.; hence to a total of l60+80=240 kw., and the overall efficiency will become 83.5%. This is a very high efliciency for a tetrode operated as a linear amplifier. FIG. 1 shows typical current and voltage conditions at the correspondingly identified points shown in FIGURE 2. The signals are shown only by way of example and many other variations are also possible.

FIG. 2 shows a basic circuit diagram of the invention. A source of anode DC. voltage V supplies a voltage of 9500 volts to operate the output tube R0 as well as the auxiliary tube R0 The tube R0 is fed from a source of double the carrier frequency, 2 f0, and produces, in an overvoltage or limiting condition, the additional anode AC voltage v of 5500 volts. This is taken from a tap 7 on a tuned circuit 3 which is coupled to the output electrode 4 of tube R0 In view of the overvoltage operation, and the fact of being operated from the same source of voltage, with about 2500 volts at the plate 4 of R0 the alternating voltage as well as its relationship to the direct voltage will remain constant even under load variations. The supply of the screen grid 2 of the tube R0 with an alternating voltage v of 1000 volts is accomplished by means of a coil SP which is coupled to the tuned circuit 3.

The effective load resistance R is coupled to the anode output circuit 5 of the operational tube R0 which circuit is tuned to the operating frequency. Care should be taken that the auxiliary voltage v of twice the frequency is applied with the proper phase to the anode 1 of the output tube R0 and that it is bypassed around the load resistance R via capacitor 6 in tuned circuit 5, and that the signal frequency AC. voltage of the tube R0 is also applied to the anode 4 of the auxiliary tube R0 to maintain the desired efiiciency.

FIG. 3 shows an input transformer TR which, on the secondary side, supplies the grids 8 and 9, respectively,

3 tubes R and R0 as well as to the cathode 14 of tube R0 The center of the primary winding of the output transformer TR is coupled to the source of DC. operating voltage, +V.

The additional amplifier consists of the tube R0 whose 5 grid is applied to the connecting point of the outputs of two rectifiers G and G with the inputs thereof being connected to the grids 8 and 9, respectively, of the tubes R0 and R0 The anodes 10 and 11 of the two tubes are connected through the secondary winding of a phasereversing transformer TR to the operating D.C. voltage +V. The sum of both the anode D.C. voltage +V and the AC. output voltage v of the additional amplifier R0 as combined in transformer TR is applied to the center of the primary winding of transformer TR The alternating and direct voltages v and V respectively, are chosen so that the sum results in only positive values, and that the zero reference level is reached at the maximum amplifier output. The curve of the anode supply voltage for the tubes R0 and R0 during the respective anode-current flows, will correspond to a rectified sinewave of twice the input flequency whose magnitude is chosen so that, upon subtraction of the effective anode-AC. voltage, at every point there will still remain a minimum positive potential at the anode of the tube.

When considering the mode of operation of the pushpull class B tubes, the following voltage will be applied to the anode during a half period:

V -]v V cos x=A cos x V cos x: (A V cos x When designating V =Pv.A (p =voltage-utilization factor), then V =A (1p cos x.

Upon the inset of the alternating current I=A cos x, the power loss Since N only appears during a half-period there will result the following:

The useful output N will result as follows:

1 Ro =zA Azp and the efficiency N N+N,

Of course, the total efficiency of the tubes R0 and R0 is likewise 1 =p As calculated from there will result the direct-current output as received by the tube:

From the power output N ipv l -2 there may be calculated 4N TZ in other words, the useful output N is produced with a direct-current input pv pv and correspondingly also the power input which results from v a(de) P Pv and the power loss of the tube 2- 2 pv a (do) 2 2 2 pv a(de)' 2' 2' anc) When placing p of the main amplifier equal to p of the additional amplifier, then the total efiiciency will be obtained from From the above table it may be seen that a considerable improvement of efliciency can be achieved when employing the circuit arrangement according to the invention. Another advantage of this circuit arrangement resides in the fact that operation of the class B amplifier tubes with both direct and alternating voltages achieves a higher peak operating voltage than for pure directvoltage operation, and due to the high efiiciency, it is possible to attain a higher output power.

The full-wave rectifier arrangement comprising diodes G1 and G2 as shown in FIG. 3 may be replaced by an additional amplifier having two tubes, Ro and R0 (FIGURE 4) whose grids 16 and 17 are each respectively connected to one grid 8 and 9 of the tubes R0 and R0 The anodes 18 and 19 thereof are connected together and are applied in common to the primary winding of the phase-reversing transformer TR Such a circuit arrangement as shown in FIG. 4 which includes tubes Ro and R is a direct replacement for the combination comprising diodes G1 and G2 and tube R0 of FIG. 3.

FIG. shows the employment of the inventive circuit arrangement in connection With a high-frequency resonance amplifier which is designed as a quiescent pushpull amplifier. The circuit arrangement of the amplifier comprising the tubes R0 and R0 resembles that of FIG. 3, but at both the input and the output of the amplifier there are circuits 20 and 21, respectively, which are tuned to the operating frequency, and at the output of the additional amplifier R0 there are further oscillatory or tuned circuits or a network 22 for use with an additional amplifier having double the operating frequency, through which the A.C.-voltage components are transmitted. The center of the high-frequency transformer TR of the additional amplifier is connected to the source of operating DC. voltage +V. In the line L extending to this source of voltage there may now be arranged the secondary winding of a further output transformer TR which is supplied by a low-frequency amplifier R0 R0 of a type similar to that shown in FIG. 3, for supplying the modulation signals. This push-pull amplifier comprising tubes R0 and R0 likewise comprises an additional amplifier R0 In the case of high-frequency quiescent push-pull amplifiers it is possible that by use of the additional amplifier and the full-wave rectification, only the most significant AC. voltage components with the desired amplitude values are transmitted. It is also important to take care that the anodeoperating voltage curve will have no effect upon the anode-current curve. In the example, therefore, the anode network 22 of the additional amplifier has been provided with resonant response points tuned for the second and the fourth harmonic of the carrier frequency f The novel mode of dynamic operation thus permits achievement of higher peak-anode voltage than would be possible in the case of pure DC. voltage operation, and results in a higher amplifier output. The illustrated embodiments are not to be construed as limiting the invention to the exact forms or uses shown and many other variations may be made in the design and configuration Without departing from the scope of the invention as set forth in the appended claims.

I claim: 1. An electron tube amplifier circuit comprising: first amplifier means; means applying an input signal of a first frequency to said first amplifier; second amplifier means; means supplying a signal of twice said first frequency to said second amplifier; means supplying direct operating potential to the out put elements of said first and second amplifier; means for combining an output signal from said second amplifier of twice said frequency with said direct potential supplied to said first amplifier output element; and

load means connected to said first amplifier output element.

2. The device of claim 1 wherein said first amplifier means comprises a first electron tube having a first input electrode and second and third electrodes, said input signal being applied to said first input electrode, and means applying said direct potential combined With a portion of said second amplifier output signal to said second electrode.

3. The device of claim 1 wherein said signal of twice said first frequency and said direct potential are dimen sioned such that said second amplifier is operated in a saturated condition.

4. The device of claim 3 including means for tuning said load to present a relatively high impedance to said first frequency and a relatively low impedance to twice said first frequency, thereby transferring energy to said load at substantially only said first frequency.

5. The device of claim 4 wherein said direct operating potential and said second amplifier output are dimensioned such that said first amplifier conducts during only one half the cycle of said first frequency.

6. The device of claim 5 wherein said first amplifier comprises a push-pull amplifier, and wherein said direct operating potential and said second amplifier output are dimensioned such that each half thereof conducts during one half of said cycle.

7. The device of claim 6 including transformer means coupled to said direct potential, and to said first and second amplifier outputs for combining said output signal from said second amplifier with said direct potential for said first amplifier.

8. The device of claim 7 including a full wave rectifier coupling said first signal means to the input of said second amplifier for supplying said signal of twice said frequency.

9. The device of claim 7 wherein said second amplifier comprises a push-pull amplifier connected to said first signal means to supply said signal of twice said frequency, and having the anodes connected together to said transformer means.

10. The device of claim '7 wherein said direct operating potential and said second amplifier output are dimensioned such that said second amplifier conducts during only one half the cycle of said first frequency.

11. The device of claim 7 including circuit means for tuning the input and output signals of said push-pull amplifier to the first frequency and for tuning the output of said second amplifier to twice said first frequency.

References Cited by the Examiner UNITED STATES PATENTS 9/1940 Terman 330-128 X 5/1949 Harris 330-123 

1. AN ELECTRON TUBE AMPLIFIER CIRCUIT COMPRISING: FIRST AMPLIFIER MEANS; MEANS APPLYING AN INPUT SIGNAL OF A FIRST FREQUENCY TO SAID FIRST AMPLIFIER; SECOND AMPLIFIER MEANS; MEANS SUPPLYING A SIGNAL OF TWICE SAID FIRST FREQUENCY TO SAID SECOND AMPLIFIER; MEANS SUPPLYING DIRECT OPERATING POTENTIAL TO THE OUTPUT ELEMENTS OF SAID FIRST AND SECOND AMPLIFIER; MEANS FOR COMBINING AN OUTPUT SIGNAL FROM SAID SECOND AMPLIFIER OF TWICE SAID FREQUENCY WITH SAID DIRECT POTENTIAL SUPPLIED TO SAID FIRST AMPLIFIER OUTPUT ELEMENT; AND LOAD MEANS CONNECTED TO SAID FIRST AMPLIFIER OUTPUT ELEMENT. 